1. Field of the Invention
The communications industry""s conversion from electrical to optical communications engineering has accelerated the demand for and the requirements of optical transceiver modules in all fields of data transmission. Both high-rate optical transmission technology on long-distance lines via glass fibers, as well as optical transmission technology with comparatively lower data rates via relatively xe2x80x9cthickxe2x80x9d polymer fibers or hybrid glass/polymer fibers (so-called HCS fibers), are increasingly used. In the former case, hundreds of kilometers are typical, whereas only some 10 to 100 m are transmitted at data rates of a maximum of some 100 MB/s in the latter case. Systems of this second type are used within mobile means (motor vehicles, railway, airplanes) or for the so-called in-house linkage, i.e., within a building, such as for the data connection of all multi-media devices existing in a house (TV, internet, video recorder, audio devices, PCs, etc.). For cost reasons these networks do often not operate with laser diodes but instead are operated using simple surface light emitting light diodes (LEDs). For coupling such an LED to a relatively thick optical waveguide, a very inexpensive structure may be used, although significant precision is still required. An electro-optical module that contains the coupling point from the LED transmitter to the waveguide or from the photo diode receiver to the optical waveguide, is called optical transceiver.
2. Technical Background of the Invention
For a coupling of a surface-emitting LED and a relatively thick polymer fiber optical waveguide, generally two constructions exist, namely constructions without beam formation and constructions with beam formation. It is noted by way of non-limiting example that typical dimensions may be 250xc3x97250 xcexcm2 for the LED and 1000 xcexcm diameter for the polymer fibers. Beam formation means that some or all of the light rays emitted by the LED are changed in their propagation through lenses or curved mirrors so that a higher light portion can be coupled into the optical waveguide compared to a case where such measures are not taken. In any case, the alignment of the optical waveguide to the LED requires a high precision in view of the relevant dimensions, such as those given by example above.
One approach for this type of coupling is presented by the MicroMID technology which has recently become known. An example of this technology is described in DE 198 51 265 A1. Here, a micro-structured plastic support is used, the shape of the support being capable of being designed very flexibly. The manufacture of a reflector for the LED while simultaneously manufacturing an electronic circuit on the substrate is possible. An adjustment of the optical waveguide is implemented by means of a three-dimensional structure formed on the substrate. However, the high equipment costs of this technology are disadvantageous so that only the manufacture of large numbers of pieces justifies their use. Finally, since in the MicroMID technology the electronic circuit of the transceiver must be imaged in conformity with the injection molding tool, the technology is cumbersome in attempting to adapt to client-specific variants of the circuit. An adjustment is implemented between LED and optical waveguide in a structure ordered from LED to micro-structured printed circuit board to fiber plate to optical waveguide. Publications with respect to the MicroMID process can be found in Kragl, H. et. al.: xe2x80x9cMICROMID: A low cost fabrication technology for polymer fiber transceiver modulesxe2x80x9d, POF Conference 2000, Boston, and in Kragl, H. et. al.: xe2x80x9cMicrostructured three-dimensional printed circuit boards: a novel fabrication technology for optical transceiver modulesxe2x80x9d, Proc. MicroTec 2000 Conference, Hannover.
For coupling an optical fiber and an LED, a coupling device where the LED optically opposes the end face of the fiber is known from DE 38 34 395 C2. The LED is fixedly connected to a support and is electrically connected by a bond wire to a conductor formed on the support. A coupling element is connected to the support and receives the end portion of the optical fiber. The LED is directly arranged on a planar electrode, namely a so-called lead frame. The coupling element receives the end of an optical fiber, the optical fiber having a free end face to be opposed to the LED, the coupling element having a type of a column which comprises sections matching with the conductors of the lead frame, so that these conductors are received in the sections. The LED is attached on the one conductor, whereas the other conductor is connected to the LED through a bond wire. In order to attach the LED on the lead frame in a highly precise manner, an optical pattern detection process is required, which proceeds so slowly that a use in mass production must be ruled out. If, however, the placing of the semiconductor element is left to a mass die bonder, a tolerance in the range of 50 xcexcm to 70 xcexcm must be accepted. When attaching the coupling element to the lead frame, there is some likelihood that the lead frame will be damaged, and the bond wire can be damaged even more easily. If this is to be avoided, additional tolerances must be taken into consideration so that, in the case of mass production, an overall tolerance of 200 xcexcm must be taken into consideration.
A coupling arrangement for coupling an optical waveguide to an opto-electronic device, e.g. a light emitting diode or a photo diode, is known from EP 0 611 975 A1. This coupling arrangement uses a cuboid base member made of a silicon monocrystal and a cuboid cover member also made of a silicon monocrystal, the cover member planarly lying thereon. A V-shaped groove for receiving the uncovered end of an optical waveguide is formed in the base member, the groove ending in a reflecting, oblique surface inclined by 45xc2x0. On the end of the groove opposite to the oblique surface, this groove opens into a V-shaped groove of a larger cross section, which provides for the accommodation of the covered section of the optical waveguide and which extends up to an edge of the base member. In the area over the oblique surface, the opto-electronic device is attached on the base member. The cover member comprises on its side facing the base member a V-shaped groove whose cross section corresponds to the larger cross section of the V-shaped groove in the base member. In the area in which the semiconductor component is located, the cover member has a recess, which offers space for the accommodation of the opto-electronic device. The orientation of the base member and the cover member on each other is carried out by means of two spheres, which are received in matching pyramid-shaped recesses formed in the base member and in the cover member. The cover member has two openings through which a casting compound can be filled into the area of the electro-optical device and the covered optical waveguide. This publication does not provide any clue regarding how the opto-electronic device is aligned on the reflecting oblique surface to obtain the desired accuracy that is defined by +/xe2x88x921 xcexcm.
A laser-glass fiber coupling and a method of establishing such a coupling connection is known from DE 33 39 189 A1. In this coupling arrangement, the coupling point is encapsuled with a curing resin mass to obtain optically favorable relations and to obtain a device for coupling a semiconductor and a fiber optical waveguide that is insensitive against environmental influences.
An optical coupling between an optical semiconductor and a fiber optical waveguide is known from U.S. Pat. No. 6,004,046. This arrangement uses a paraboloid mirror, not only bundling the light rays emitted by the optical semiconductor, but also at the same time deflecting them by 90xc2x0.
An object of the invention is to provide a coupling arrangement for optically coupling an end of an optical waveguide with at least one electro-optical or opto-electrical element and a method suitable for the manufacture thereof, so that a light-emitting and/or light-receiving semiconductor component may be aligned in a highly precise alignment achieved in a technically simple manner.
According to an aspect of the invention, an optical coupler for optically coupling an optical waveguide, having an end portion, with at least one electro-optical or opto-electrical semiconductor element that optically opposes an end face of the end portion, the optical waveguide being insertable into the optical coupler, includes: a support having at least one conductor formed thereon; at least one semiconductor element disposed to optically oppose the end face of the waveguide, the semiconductor element being fixedly connected to the support; a bond wire electrically connecting the semiconductor element to the conductor; a coupling element connected to the support and adapted to receive the end portion of the optical waveguide; a submount having a top and bottom side, the submount being fixed at its bottom side to the support, the submount having on its top side an adjustment structure in the form of a recess adapted for precise adjustment of the semiconductor element; and a transparent adhesive, wherein the semiconductor element is fixed in a thermally conductive manner to the submount, the coupling element is positively aligned on the submount, at least that conductor of the support onto which the bond wire is connected is electrically isolated from the submount, and wherein a space, between the semiconductor element and the end face of an optical waveguide to be inserted, is adapted to be filled by the transparent adhesive.
According to another aspect of the present invention, a coupling arrangement includes: a waveguide having an end portion including an end face; a support having at least one conductor formed thereon; at least one semiconductor element, the semiconductor element being one of an electro-optical type and an opto-electrical type, the semiconductor element being disposed to optically oppose the end face of the waveguide, the semiconductor element being fixedly connected to the support; a bond wire electrically connecting the semiconductor element to the conductor; a coupling element connected to the support and adapted to receive the end portion of the waveguide; a submount having a top and bottom side, the submount being fixed at its bottom side to the support, the submount having on its top side an adjustment structure in the form of a recess adapted for precise adjustment of the semiconductor element; and a transparent adhesive, wherein the semiconductor element is fixed in a thermally conductive manner to the submount, the coupling element is positively aligned on the submount, at least that conductor of the support onto which the bond wire is connected is electrically isolated from the submount, and wherein a space between the semiconductor element and the end face of the waveguide is filled by the transparent adhesive.
In various embodiments of the invention, the coupling arrangement may be adapted so that the end portion of the waveguide is able to be inserted into the recess of the submount without tolerance. An optical path may be defined for the semiconductor element, and the coupling arrangement may include a beam-forming metallic reflector surrounding the optical path of the semiconductor element, the beam-forming metallic reflector being arranged between the semiconductor element and the end face of the waveguide. The reflector may include a metal layer disposed on surfaces of the submount surrounding the semiconductor element. The reflector may include a metal layer formed on a wall of the coupling element between the end face of the waveguide and an end portion of the coupling element adjoining the semiconductor element. The reflector may include a metal layer formed on a wall of the coupling element between the end face of the waveguide and an end portion of the coupling element adjoining the semiconductor element. The coupling arrangement may also include at least one cutout for accommodating at least one bond wire extending from the semiconductor element, the cutout being formed in at least one of the coupling element and the submount. In an optical coupling arrangement, the optical path may be further defined as being between the semiconductor element and the end face of the waveguide, and the reflector may be formed to deflect the optical path by 90xc2x0. The waveguide may include a glass fiber. The end portion of the waveguide may be inserted so that it adjoins the semiconductor element, and the end portion may be adapted to be held by a highly precise ferrule receivably disposed in the recess formed in the submount. The submount may be electrically conductive, the semiconductor element may be electrically connected to the submount, and the bottom side of the submount may be electrically connected to the support. These exemplary embodiments, those discussed below, and others may be employed for obtaining various advantages.
In various additional exemplary embodiments, the invention provides an arrangement for optically coupling an optical semiconductor element, e.g. a transmission diode, to an optical waveguide having a submount on which the semiconductor element is positioned. The submount and the coupling element may contain beam-forming reflectors. The submount may be directly set onto a support, which may, for example, be a conventional printed circuit board, a TO housing, a lead frame, or a Molded Interconnect Device (MID) support. At least one bond wire is guided from the semiconductor element onto the support, which, if it is not conductive itself, is provided with a conductor to which the bond wire can be connected. An adjustment of the optical waveguide with respect to the semiconductor element may be implemented by adjusting the optical waveguide at the submount, either directly or by means of a separate coupling element, which in turn may be aligned precisely onto the semiconductor element by interlocking connection with the submount.
The submount may be made of a metal or of plastic with a surface metallization and it may directly establish the electrical connection between the support and an electrode of the semiconductor component. It may also be made of an insulating material, such as microstructured ceramics. In any case, is it favorable if the submount is heat-conductive in order to favorably discharge the heat emitted by the semiconductor component. It is evident that if the submount does not serve for the electrical connection to one of the electrodes of the semiconductor component, the semiconductor component may alternately be electrically connected by means of at least two bond wires.
The coupling element may be particularly used for coupling fiber conductors and in that case preferably consists of a thermoplastically-made plastic body with a cylindrical bore in an upper, first segment, which may taper in a second, lower segment in the form similar to a paraboloid of rotation. In such a case, the inner wall of the paraboloid may then advantageously be coated in a reflecting way, e.g., by coating with a thin silver layer. As an alternative, the coupling element may be formed as a massive metal member, e.g., made of silver, aluminum or copper, the latter preferably being formed with a reflecting coating made by deep drawing. In the case of higher volume manufacturing runs, the deep drawing of parts of soft metals may be more inexpensive than the injection molding of such parts.
Regarding the above-mentioned exemplary embodiment having a paraboloid form, a recess may be formed on the base point of the paraboloid, the edge contour of the recess being substantially congruent with the outer contour of the submount. Such a structure may be used to positively accommodate the submount and to thereby align the coupling element at the submount. Moreover, it may have at least one recess for receiving one or several bond wires, the latter being used, for example, when the submount is used for insulating as noted above.
In another exemplary aspect of the present invention, an assembly of a coupling device may include the following steps. A first step may include attaching a submount on a support having a surface suitable for wire bonding at a position provided for this purpose. The submount, for example, may be soldered or adhered-on with conductive adhesive. An attachment may be made by use of a projection (e.g., a pin) formed on the submount on the side opposing the semiconductor component, the projection being seated and secured in a recess or hole. The semiconductor element may be attached onto the submount by use of die bonding where, depending on the required precision, an adjustment structure arranged in the submount may be used. A second step may include electrically connecting the semiconductor component to a conductor on the support by wire bonding starting out from the semiconductor component. When using a coupling element, the coupling element may be set onto the submount and aligned in a manner that allows the semiconductor component to look through an opening of the coupling element provided for this purpose. The coupling element may have an adjustment structure allowing it to be precisely fit onto the submount, thereby exactly positioning the semiconductor component. Of course, damage of the bond wire or the bond wires must not occur during adjustment. In order to avoid the danger of a bond wire damage, the submount may also have a lateral bond wire protection or any other suitable manner of protection. In a preferred embodiment, when the coupling element is correctly seated on the support, it is non-detachable and is preferably impervious to fluids that may be present in this position, such as fluids used for manufacturing the support and the submount, e.g., by adhesion. A third step may include inserting a transparent adhesive into the submount, such as by filling. This may be achieved, for example, by filling the submount the fiber guide hole of the coupling element, the adhesive also flowing into the section in which the bond wire extends, thereby also enclosing the bond wire there. A fourth step may include inserting the optical waveguide so that its end is brought into contact with the adhesive whereby it is adhered to the adhesive that is still soft. If a coupling element is missing, the optical waveguide directly aligns at the submount. If a coupling element is used, the alignment at the submount may be carried out by use of the coupling element. As an alternative, it is also possible to use a plug of a non-adhesive material instead of using the optical waveguide, such a plug staying at its position until the adhesive has cured and being then replaced by the optical waveguide. This alternative allows the optical waveguide to be exchanged at a later time.
In a preferred method of assembly, if a suitable projection is being provided in the coupling element or at the submount (for example, when an annular shoulder is provided in the coupling element) where the end face of the optical waveguide abuts when being inserted, a significant improvement may be achieved in assembly, since the exact, axial position of the optical waveguide no longer need to be observed. This also represents a substantial improvement compared to the MicroMID technology, which does not provide a passive, axial adjustment for the optical waveguide. When inserting the optical waveguide or the plug, excessive adhesive may escape past the optical waveguide or plug. As an alternative, a vent hole or other means suitable from the field of casting technology may be provided, which takes up excessive adhesive that is displaced from the optical waveguide or plug when the optical waveguide or plug is inserted.
The submount and/or the coupling element may be provided with optical reflectors by suitable shaping and coating.
A circuit arrangement used for operating the semiconductor element (e.g., LED and/or a photo detector to be mounted in the same manner) may directly be attached in direct proximity of the semiconductor component on the support, which may for instance be a double-sided printed circuit board. For example, the circuit arrangement may be attached on the back side of the printed circuit board. Thus, for example, a pre-amplifier for a photo diode (PD) may be located only 1 mm away from the PD. EMC problems therefore may be prevented. Since the printed circuit board is typically manufactured in a conventional standard industrial process, the wiring provided thereon may be implemented in any complex manner. High-quality printed circuit boards, such as those made using ceramics or printed circuit boards made of Teflon, particularly necessary for extremely high-frequency applications, may be used.
In order to obtain a complete transceiver system, a coupling element with a flexible printed circuit board may be fit into an electric plug system and the optical waveguide ends may be connected via a splice or plug system. Alternatively, the coupling element with a rigid printed circuit board may be directly inserted into a female plug, wherein the plug contacts are realized (e.g., by contacts on the printed circuit board).
The present inventor has achieved improvements in optical coupling arrangements. Contrary to the known MicroMID process, the optical waveguide of the present invention is not adjusted at the support (e.g., printed circuit board) but at the submount carrying the semiconductor element, this being done directly or by use of the above-mentioned coupling element. If the submount is a metallic or metallized body, it typically does not have the power guidance demanded from a support (e.g., printed circuit board) for both electrical terminal conductors, but only for one of them. On the other hand, by adjusting via a submount, advantages result compared to the MicroMID technology.
As a result of the present invention, a printed circuit board to be newly designed for a given product application does not have to be realized in the expensive MicroMID process having high equipment costs. In addition, the adaptation of the outer electronic connection on a standard printed circuit board requires substantially shorter development times and is less expensive.
By galvanically applying a copper layer having a thickness of 25 to 50 xcexcm on the MicroMID printed circuit board, the micro-structured plastic surface of the MicroMID substrate substantially loses precision. By comparison, a micro-structured submount according to the invention may have highly precise adjustment structures on its surface and may include a massive or sheet-like metal or metallized plastic element. The invention thus may provide for a significantly higher precision compared to MicroMID.
The structures on the micro-structured submount that can be used for adjusting the optical semiconductor element do not necessarily have to be formed with significant de-formation bevels, since they are not required to be manufactured in a multi imaging process in metal and plastics. Thus, vertical structures are also possible. If a micro-structured submount in the shape of a sheet having thickness of approximately 100 xcexcm is used, the opening for the semiconductor element can easily be expanded by bending the sheet so that the semiconductor element can be inserted. Subsequently, the fine centering of the semiconductor element may take place during the relief phase.
On a metallic, micro-structured submount, the electro-optical semiconductor element may also be soldered instead of only being adhered as in MicroMID. This leads to a thermally and electrically improved connection between the semiconductor component and the submount, which is particularly important when the semiconductor component is a LED having a bad efficiency, whose lost heat must be dissipated.
In MicroMID technology and in the classic lead frame technology, the entire metal surface of the substrate or of the lead frame may be wire bonded. A surface coating suitable for this purpose is expensive (e.g., palladium support) and particularly has the disadvantage that the optical reflection behavior of the layer is not optimal. A non-bondable silver layer would have a better reflection factor for many applications but it cannot typically be used for the above-mentioned reason. Since, however, it is generally not necessary in the present invention to wire-bond on the submount, this submount can be provided with an ideally reflecting coating, which does not have to take bondability into consideration.
If the substrate of the semiconductor element is non-conductive, so that a direct electrical contacting of the same at the submount is not possible, an electrical connection between the semiconductor component and the support may be implemented, while the other electrical connection between the semiconductor component and the support may be implemented directly on the support by means of wire bonding.
In additional embodiments of the invention, a number of variants are possible and sensible, and may have an advantageous effect independent of the required precision and/or independent of the irradiation properties of the transmitting diode.
The following non-limiting examples illustrate variations for a coupling arrangement according to the invention. For example, a waveguide layer may be formed of a planar plate and a curved plate, a waveguide layer may be formed as a tube, a plurality of semiconductor elements may be optically coupled to the waveguide layer, semiconductor elements may be transmission diodes of different light emission wavelengths, a semiconductor element may be electrically connected to the submount by a use of die bonding, a beam-forming metallic reflector may be formed to surround the optical path and may be arranged between the semiconductor element and the end face of the optical waveguide, the reflector may be formed as a metal layer on the surfaces of the submount surrounding the semiconductor element, the reflector may be formed as a metal layer on a wall of the coupling element between the end face of the optical waveguide and an end portion of the coupling element adjoining the semiconductor element, at least one recess for accommodating a bond wire connecting the semiconductor element with a circuit may be formed in the coupling element, at lest one recess for receiving a bond wire connecting the semiconductor element with a circuit may be formed on the submount, the reflector may be formed to deflect the optical path between the semiconductor element and the end face of the optical waveguide by 90xc2x0, the submount (1) may be a lathe work, the submount may be a punched member, the coupling element may be a deep drawn member made of a soft metal, the optical waveguide may be a glass fiber having its end portion adjoining the semiconductor element held by a highly precise ferrule, the ferrule may be adapted to be inserted into the coupling element, the ferrule may form the coupling element and an end of the ferrule may be received by a recess formed in the submount, and an electro-optical transmission converter and an opto-electrical receiver converter may be attached on the submount so that they are shielded from each other and so that the converters optically oppose the same optical waveguide.
Many variations may likewise be used in forming a coupling arrangement according to the present invention. Some non-limiting examples of methods that may be used in forming the coupling arrangement include: manufacturing the submount by a micro-structuring method that includes applying a thin conductive coating on the surface of a micro-structured plastic body, removing projecting sections from this coating by surface polishing, applying metal on the remaining conductive coated surfaces by use of galvanization, and removing this metal structure from the plastic body; a method of manufacturing a coupling arrangement, for optically coupling an end of an optical waveguide with at least one electro-optical or opto-electrical semiconductor element that optically opposes the end face of the optical waveguide, may include the steps of (1) using a two-piece tool to form a cavity that images the coupling element receiving the end portion of the optical fiber, the tool having one part formed as a negative image (e.g., impression) of a submount receiving the semiconductor converter, (2) forming a molded body by injecting a plastic material into the cavity, the molded body being shaped later, (3) metallizing an entire surface of the molded body on its side negatively imaging the submount, (4) removing the metallization by brushing on all projecting portions; (5) increasing the remaining metallization by galvanic metal deposition, (6) separating the metal structure formed on the molded body from the molded body, (7) providing the resulting molded body with a light inlet opening on the bottom of a recess that is determined for receiving the optical waveguide, and setting the molded body onto the submount formed as a coupling element receiving an optical waveguide; a method as just described for forming a coupling arrangement, the method including removing ridges from the metal structure after the galvanizing, and optionally including metallizing the recess, determined for receiving the optical waveguide, in its area adjoining the bottom; a method, for optically coupling a fiber optical waveguide with an electro-optical or opto-electrical semiconductor component mounted on a submount, may include aligning the submount with a coupling element having a bore aligned onto the semiconductor component, filling the space above the semiconductor component and above part of the bore with a transparent adhesive, then inserting the fiber optical waveguide into the bore and curing the adhesive in contact with the end face of the fiber optical waveguide; and, a method of optically coupling the end of a fiber optical waveguide to an electro-optical or opto-electrical semiconductor component mounted on a submount, at which a coupling element is aligned, the method including aligning a bore of the coupling element with the semiconductor component, filling a space above the semiconductor component and part of the bore with a transparent adhesive, then inserting a plug of a non-adhesive material into the bore and curing the adhesive in contact with the end face of the plug, removing the plug from the bore, and then inserting the end of the fiber optical waveguide into the bore.
Any reference herein to a LED or transmission diode as being a semiconductor element shall not be understood in a restrictive way but only as an example, since the present invention may also be used in a same or similar manner in connection with light-receiving semiconductors such as photo diodes, photo transistors or photo resistors.